Expansion tank Q

[Boomy]

On my pre lit 1700 Xflow it has an expansion tank set as high as it will go really and so far the car has never overheated and only ever touched the 100 mark on the temp gauge once in hot weather.

My question however is should the expansion tank always  be on the full level or will it just dump water into and out of it as and when it needs to?

At the moment, i top it up to full and after a few blats it is down to the minimum mark or just under and there is a small puddle under the car the following morning.

I found a small hole in a tube when i first got it so sorted that and assumed that was the end of my problems, however again i topped the bottle back up to full and it is now down to just under the minimum again with evidence of water under the car on the garage floor.

If i remove the filler cap at the front of the engine (not the one on the expansion tank which sits just under the windscreen) however it is almost full to the top.

So, either i do have a leak somewhere else, or is is just finding its own level and dumping out some excess water due to me overfilling it by topping it up to the max level in the expansion tank?

All the hoses seem leak free and i'm really not sure where any other signs of wetness around the bottom of the engine would be coming from!

I was coming to the conclusion that in most factory cars (ford vauxhall bmw etc etc) they are obviously built in such a way that any expansion bottles are designed to always be on the full mark, but with kit cars that may all go out the window?

Any advice appreciated as usual, it's bugging me now as to what i should do next.It may also be worth mentioning that i did change the coolant not so long ago, it was very clean when it all came out and there seems to be no air locks now it is full again.

[Mark Stanton]

All I can say with both my engine fitments - that I fill up the expansion tank to the max mark - drive it - when checking the level it has returned to it original mark - no overheating issues   and no puddles or drips

Some expansion tanks have a Max Hot and a Max cold marking - does yours

[Darren B]

Hi Boomy,

My understanding of the water system is that it is pressurised, hence the ability for it to reach temps above 100 and not boil the water away (mine gets to 105 in traffic).  I fill my car to the max mark on the expansion tank, and when running it rises about 2-3cm above that level, but when cold it returns to the original level.

You shouldn't end up with a puddle under the car and any leak will potentially compromise the efficiency of your system.

Have you recently refitted any hoses?  I replumbed mine and it took two heating/cooling cycles to get all the hose clamps torqued up correctly as they expanded and contracted.

Darren  

[Boomy]

Thanks for the replies.It just seems odd to me that is seems to only stay around the minimum mark or just under.

Maybe a few more local runs are in order to 100% confirm this.

Will let you know how it goes once i get my dashboard back on.Project carbon fibre hit a few glitches today

[Martin Keene]

What cap is fitted to the thermostat housing? It should be a blank cap to allow water to run freely to the header tank.

[Boomy]

This is the current setup.The cap at the bottom of the pic is one of them twist jobbies with the spring underneath.

[Martin Keene]

There's your problem... A spring underneath means it's a pressure cap not a blanking cap which you need.

Edited to add: PM me with your address and I'll chuck an old one I've got in the post.

[Major Stare]

PM me with your address and I'll chuck an old one I've got in the post.

I think i have one lying around in the garage, PM me if you need it.

I dont run a header tank on my X-Flow now after a bit of a tidy-up/re-design last month. Watch WW Mag soon for details.

[Boomy]

Thanks guys.PM sent to Mr Keene for the moment as he mentioned it first but thanks for the offer Major.